Summary Although sucker-rod pumps are installed in nearly 90% of all oil wells and many gas wells (for liquid unloading) in the United States and have been widely used for decades, there are many issues regarding their hydraulic performance that are not well understood. This is caused by the difficulty of obtaining downhole pump-performance data. Many persistent problems in sucker-rod pumping, including partial pump fillage, gas interference, gas locking, fluid pound, sticking valves, rod downstroke compression loading, equipment failure, reduced production, etc., are difficult to diagnose from the surface. Currently, verification of sucker-rod pump problems can only be inferred by removing the pump at great expense. Thus, root-cause analysis depends on guesswork and component analysis. Knowledge of pump characteristics downhole would allow problems to be predicted rather than simply diagnosed after they have persisted long enough to result in failure. To develop a knowledge base on sucker-rod pumps, a two-fold approach is being pursued: instrumentation of a clear sucker-rod pump in the laboratory, followed by the development of an instrumented downhole pump. The laboratory pump allows the development of diagnostic techniques in which pump performance can be verified visually. The downhole pump will allow testing at field conditions. A key element to both the laboratory and downhole instrumented pumps is measuring the compression chamber pressure (pressure within the pump barrel). The instrumentation has been designed to collect high-speed (100 samples a second) data so that transient behavior (ball chatter, etc.) can be observed. Data is archived while the pump operates under various conditions, from full to pumped off. This paper presents results of tests with the laboratory pump that have resulted in new insights about pump friction and the techniques developed to measure dynamic and static pump friction. Analyses of the compression-chamber pressure are leading to a better understanding of what happens when both valves are closed and leading to the development of techniques to perform real-time diagnoses that determine fillage and gas locking. The laboratory data showed that compression-chamber data can be insightful in understanding pump conditions. Introduction The oil and gas industry continues to rely on sucker-rod pumping systems as the principal method of artificial lift for fields in which the reservoir pressure has been depleted and development of economic flow rates requires drawing the bottomhole pressure to the lowest possible level. Lifting costs represent one of the major operating expenses in these fields, and, thus, producers should maintain every pumping system at the maximum efficiency with a minimum of downtime and a long time between failures. Analysis of the pumping system's performance relies on surface measurements of load, position, and acceleration of the polished rod, prime mover power, pressures at the casing and tubing heads, and fluid level in the annulus. These measurements are used to characterize operation of the downhole pump, the rod string, and the surface equipment based on a simplified theoretical description of the dynamics of the fluid and the mechanical system. Early attempts by Gilbert 1 to verify the validity of this approach resulted in the development of the pump dynagraph, which allowed recording of the pump pressure during a pump stroke by installing a specially designed instrument above the pump plunger. Results of this work were vital for the development of accurate design and analysis procedures, such as the API RP 11L method,2 and the later development of numerical simulators of pump performance3 for design and analysis. To validate modern approaches to modeling the pumping system, the industry undertook a study to verify the calculated results by downhole measurement of rod loads. This resulted in a database of measurements for various wells and conditions that can be used by software developers to verify the formulation and solution algorithms applied in their programs.4,5 This study resulted in significant improvement in understanding mechanical rod forces. However, there is still little understanding of pump performance under downhole conditions, particularly the relationship between the pressure of the fluid flowing through the pump and the mechanical loads developed during the pump stroke. This is the principal objective of the current study, which involves a two-fold approach - instrumentation of a clear sucker-rod pump in the laboratory followed by the development of an instrumented downhole pump for field testing. The laboratory pump allows the development of diagnostic techniques in which pump performance can be verified visually. The downhole pump will allow testing at various field conditions. Laboratory Pumping System The experiments were conducted at the artificial lift facilities of the Petroleum and Geosystems Engineering Dept. at The U. of Texas at Austin. Fig. 1 shows a schematic of the experimental well. The pumping unit and wellhead are standard oilfield components. The pumping unit is a beam-balanced unit, API 16-53-30, driven by a 1-hp electric motor that operates through a mechanical, variable-speed drive. Clear acrylic pipe was used for the casing-tubing vertical wellbore. The inside diameter (ID) of the casing is 5 in., the length is 65 ft, the outside diameter (OD) of the tubing is 3 in., and the length is 50 ft. A plastic container with a 200-gal capacity is used as storage tank for the oil. The oil viscosity used was 3.42 centistokes at 25°C, and the oil specific gravity was 0.81. The distance from the stuffing box to the seating nipple is 49.9 ft. The arrangement of the rod string from the bottom to the top is delineated as follows.The sucker-rod pump plunger = 1.79 ft × 1.765 in.One coupling=0.4 ft × 1.765 in.One 2 ft × 0.625-in. pony rod.One 8-ft × 1.125-in. sinker bar (polished rod).One 4-ft × 0.625-in. pony rod.Four 6-ft × 0.625-in. pony rods.One 8-ft × 1.125-in. polished rod. The sucker-rod pump is a 1:1 replica of a standard API tubing pump. The working barrel, with a length of 4 ft, was constructed from plexiglass to allow the inner regions to be seen. The standing valve was attached to the bottom of the tubing. The steel plunger has a smooth sealing surface with a diameter of 1.765 in., a length of 21.5 in., and a plunger/barrel clearance of 0.003 in.

Sand and other fluid entrained particulates can cause substantial operational problems for rod pumped producing wells. These problems take the form of down- hole pump wear, plunger sticking, and/or catastrophic breakage of pump components. A six year study of 600+ pump investigations shows that problems with particulates account for a substantial number of the total barrel and plunger failures. Many of these failures could have been avoided through the proper application of API and special pump designs as well as certain choices of pump variables. These pump variables and designs will be addressed along with operating parameters. How hard is sand? How large is it? Should plunger and barrel choices take these variables into account? Also, metal plungers must "slip" fluid for proper lubrication. Too much slippage leads to pump inefficiencies. However, down-hole pump efficiencies based on slippage need to be balanced against pump longevity due to proper selection for particulate production. Some time-proven rules of thumb can be applied to make these choices, and an included chart will make plunger slippage calculations simple and straightforward. Scale which sticks to pump surfaces dictates the choice of a different style down-hole pump. A straight-forward modification of an RH style API pump has proved successful in these conditions. Fluid and particulate production with and without attendant gas production requires a different approach to down-hole pump selection. Several successful older pump designs as well as some recently proven new designs will be described. A test program has been completed and actual applications have shown that an API Tubing Pump derivative can pump large volumes of particulate laden fluid without characteristic sticking of the plunger. Introduction A study was conducted of pumps with relatively short run times during the years from 1989 through 1994. These were analyzed with respect to pump barrels or plungers that had problems due to produced particulates. A significant number of the barrels and plungers developed problems due to particulate induced wear or sticking (Figs. 1 and 2). Costs of new rod pumps and pump repairs are typically closely monitored, perhaps at the expense of overall well production profitability. A different costing focus may be applicable, and appropriate record keeping is necessary for accurate cost analysis. New record keeping methods are available which pinpoint areas for improvement. Variables For Rod Pumping Several general pumping choices for the down-hole pump must be logically made for optimum functioning and efficient longevity. These apply to any pump and include; pump metallurgy, plunger minus fit choice, and slippage design for lubrication of the plunger and barrel interface. Pump Metallurgy. pump wear is the primary consideration when particulates are produced along with the production fluid. Sand grains can be as hard as hardened steel (Table 1), causing contact wear and erosion of pump surfaces. The two surfaces that receive the most wear are the barrel and plunger surfaces. These two parts of the pump form the moving surfaces of the pump that are subject to sliding wear during each stroke of the pump. During a typical 24 hour pumping day at 10 strokes per minute, a plunger and barrel will see over 14,000 cycles of up and down motion contributing to plunger and barrel wear. For a 100" long down-hole stroke length, the total distance of sliding wear is about 45 miles per day. Barrel Metallurgy. The oldest and most popular choice of inside wearing surfaces for pump barrels is hard chrome plating. The hardness is Rc67 minimum, and the chrome plating seldom wears out. Its weakness is due to its intolerance of hydrochloric acid, which is commonly used for remedial acid treatment of oil wells, and other corrosive fluids which attack the chrome plating bond line. Hydrochloric acid will dissolve chrome plating. Any down-hole formation fluid with a Ph below 7, or other corrosive down-hole fluids will eventually cause chrome plating to flake off, through weakening of the chrome to substrate bond line. This invariably leads to further damage to the barrel and plunger by the hard chrome particles which have flaked off of the barrel. This weakness is one of the reasons that chrome plating seldom wears out. It is more likely that it will eventually flake off in some area before it wears out, even if the barrel has given a satisfactory run time. Therefore, a chrome plated barrel has one likely early failure mode; flaking off of the plating, and two possible normal "used up" modes; wearing away or flaking off of the chrome plating. A significant number of the barrels represented in the failure study had problems with chrome flaking. None had problems with worn chrome. A nickel carbide coating is available for the inside and outside surfaces of pump barrels. It provides a hard wearing inside surface and an outside corrosion barrier. P. 105

Summary Conventional ball valve systems and insert-guided cages compromise performance due to gas interference, solids accumulation, and ball vibration that shortens the life and efficiency of conventional traveling and standing valve cages. The analysis of the flow profile around a common ball valve resulted in the design of a new proprietary pump system that maximizes fluid flow, creating a vortex profile that extends service life while increasing production. The proprietary vortex fluid pump system was compared against conventional inserts during in-house testing and in a laboratory flow loop. Minimum to maximum flow rates were digitally measured to calculate the pressure drop at each flow rate with and without injecting gas. The transparent flow loop tubing allowed a visual qualitative assessment of fluid flow. During laboratory testing, conventional inserts measured high ball vibration with excessive pressure drop. The proprietary vortex fluid pump system had no ball vibration, with a significant pressure drop decrease, and gas remained entrained as it cycled through a vortex flow. The results from laboratory testing showed an average 40–46% pressure drop decrease compared to conventional inserts. Laboratory data were confirmed in numerous field applications as well as four case studies from four different fields for four separate operators. The vortex fluid pump system showed greater pump efficiencies and pump longevity. After installation of the system, cumulative results were combined to show an average 46% production increase over 485 wells in North America in 1 year. The proprietary vortex fluid pump system decreases erratic velocity profile and reduces vibration in the valve system resulting in improved efficiency and reliability of sucker rod pumps. The design optimizes flow dynamics enabling the ball to remain stationary, allowing smaller and lighter balls and increasing the cross-sectional flow area in the most restrictive pump section. The design reduces solids accumulation, lessens cage wear, improves pump efficiency, and increases production. The vortex fluid pump system replaces all conventional valve systems.

Although sucker rod pumps are installed in nearly 90% of all oil wells in the United States and have been widely used for decades, there are many issues regarding their performance that are not well understood. This is due to the difficulty of obtaining downhole pump-performance data. Many persistent problems in sucker rod pumping including partial pump fillage, gas interference, gas locking, fluid pound, sticking valves, rod downstroke compression loading, equipment failure, reduced production, etc. are difficult to diagnose from the surface. Currently, verification of sucker-rod pump problems can only be inferred by removal of the pump at great expense. Thus, root cause analysis depends on guesswork and component analysis. Knowledge of pump characteristics downhole would allow problems to be predicted rather than simply diagnosed after they have persisted long enough to result in failure To develop a knowledge base of sucker-rod pumps, a two-fold approach is being pursued: first, instrumentation of a clear sucker-rod pump in the laboratory followed by the development of an instrumented downhole pump. The laboratory pump allows the development of diagnostic techniques where the pump performance can be verified visually. The downhole pump will allow testing at field conditions. A key element to both the laboratory and downhole instrumented pumps is measuring the compression chamber pressure — pressure within the pump barrel. The instrumentation has been designed to collect high-speed (100 samples a second) data so that transient behavior (ball chatter, etc.) can be observed. Data is being archived operating the pump under a various conditions from full to pumped-off. This paper presents results of tests with the laboratory pump that have resulted in new insights about pump friction and the development of techniques to measure dynamic and static pump friction. Analyses of the compression-chamber pressure are leading to a better understanding of what happens during that time when both valves are closed and to the development of techniques to perform real-time diagnosis determining fillage and gas locking. Laboratory data has shown that compression chamber data can be more insightful in understanding pump conditions.

Conventional ball valve systems and insert-guided cages compromise performance due to gas interference, solids accumulation and ball vibration that shortens the life and efficiency of conventional travelling and standing valve cages. Analysis of the flow profile around a common ball valve resulted in the design of a new proprietary pump system that maximizes fluid flow, creating a vortex profile that extends service life while increasing production. The proprietary vortex fluid pump system was compared against conventional inserts in a laboratory flow loop in over 1000 iterations with varying pressures, ball sizes and ball types. Maximum and minimum flow rates were digitally measured to calculate the pressure drop at each flow rate with and without injecting gas. The transparent flow loop tubing allowed a visual qualitative assessment of fluid flow. Laboratory data was confirmed in numerous field applications as well as four case studies from four different fields for four separate operators. During laboratory testing, conventional inserts measured high ball vibration with excessive pressure drop. The proprietary vortex fluid pump system had no ball vibration, with significant pressure drop decrease and gas remained entrained as it cycled through a vortex flow. Results from laboratory testing showed an average 40% - 46% pressure drop decrease compared to conventional inserts. When extended to field applications, the vortex fluid pump system showed greater pump efficiencies and pump longevity. After installation of the system, cumulative results were combined to show an average 46% production increase over 485 wells in North America in one year. The proprietary vortex fluid pump system decreases erratic velocity profile and reduces vibration in the valve system resulting in improved efficiency and reliability of sucker rod pumps. The design optimizes flow dynamics enabling the ball to remain stationary, allowing smaller and lighter balls, increasing the cross-sectional flow area in the most restrictive pump section. The design reduces solids accumulation, lessens cage wear, improves pump efficiency and increases production. The vortex fluid pump system replaces all conventional valve systems.